Randomly-oriented composite constructions

ABSTRACT

Composite constructions comprise a plurality of granules that are arranged together in a randomly-oriented manner. The granules each comprise an ordered arrangement of a first material phase and a second material phase, wherein the first and second material phases are each continuous, and each occupy different and distinct regions of the granule. At least a portion of the first and second material phases of each granule are in contact with one another. The first material phase comprises a material selected from the group consisting of cermet materials, polycrystalline diamond, polycrystalline cubic boron nitride, and mixtures thereof. The second material phase comprises a material that is relatively softer, e.g., more ductile, than the first material phase.

COPENDING PATENT APPLICATION

This patent application is a Continuation of U.S. patent applicationSer. No. 10/726,387, filed Dec. 2, 2003, now U.S. Pat. No. 7,243,744which is incorporated hereby in its entirety.

FIELD OF THE INVENTION

This invention relates generally to composite constructions comprisingtwo or more material phases and, more particularly, to compositeconstructions having a material microstructure comprising arandomly-oriented arrangement of particles that each comprise an orderedarrangement of two or more material phases.

BACKGROUND OF THE INVENTION

Cermet materials such as cemented tungsten carbide (WC-Co) are wellknown for their mechanical properties of hardness, toughness and wearresistance, making them a popular material of choice for use in suchindustrial applications as cutting tools for machining, mining anddrilling where such mechanical properties are highly desired. Cementedtungsten carbide, because of its desired properties, has been a dominantmaterial used in such applications as cutting tool surfaces, hardfacing, wear components in roller cone rock bit inserts, cutting insertsin roller cone rock bits, and as the substrate body for drag bit shearcutters. The mechanical properties associated with cemented tungstencarbide and other cermet materials, especially the unique combination ofhardness, toughness and wear resistance, make this class of materialsmore desirable than either metal materials or ceramic materials alone.

For conventional cemented tungsten carbide, the mechanical property offracture toughness is inversely proportional to hardness, and wearresistance is proportional to hardness. Although the fracture toughnessof cemented tungsten carbide has been somewhat improved over the years,it is still a limiting factor in demanding industrial applications suchas high penetration drilling, where cemented tungsten carbide insertsoften exhibit gross brittle fracture that can lead to catastrophicfailure. Traditional metallurgical methods for enhancing fracturetoughness, such as grain size refinement, cobalt content optimization,and use of strengthening agents, have been substantially exhausted withrespect to conventional cemented tungsten carbide.

The mechanical properties of commercial grade cemented tungsten carbidecan be varied within a particular envelope by adjusting the cobalt metalcontent and the tungsten carbide grain sizes. For example, the RockwellA hardness of cemented tungsten carbide can be varied from about 85 to94, and the fracture toughness can be varied from about 8 to 19 MPam⁻².Applications of cemented tungsten carbide are limited to this envelope.

Polycrystalline diamond is another type of material that is known tohave desirable properties of hardness, and wear resistance, making itespecially suitable for those demanding applications described abovewhere high wear resistance is desired. However, this material alsosuffers from the same problem as cemented tungsten carbide, in that italso displays properties of low fracture toughness that can result ingross brittle failure during usage.

It is, therefore, desirable that a composite construction be developedthat has improved properties of fracture toughness, when compared toconventional single phase cermet materials such as cemented tungstencarbide materials, and when compared to single phase conventionalmaterials formed from polycrystalline diamond or polycrystalline cubicboron nitride. It is desirable that such composite construction havesuch improved fracture toughness without sacrificing other desirableproperties of wear resistance and hardness associated with conventionalsingle phase cemented tungsten carbide, polycrystalline diamond, andpolycrystalline cubic boron nitride materials. It is desired that suchcomposite constructions be adapted for use in such applications asroller cone bits, hammer bits, drag bits and other mining, constructionand machine applications where properties of improved fracture toughnessis desired.

SUMMARY OF THE INVENTION

Composite constructions of this invention comprise a materialmicrostructure made up of a plurality of granules that are combinedtogether with one another in a randomly-oriented manner. The granuleseach comprise an ordered arrangement of a first material phase and asecond material phase. The first and second material phases are eachcontinuous, and each occupies different and distinct regions of thegranule.

At least a portion of the first and second material phases of eachgranule are in contact with one another. The granules can be configureddifferently so that the material phases have different shapes and sizes.In an example embodiment, the granules are configured having acentrally-positioned core formed from one of the material phases, and asurrounding shell portion formed from the other of the material phases.The core and shell are each formed from one of the first and secondmaterial phases.

The first material phase comprises a hard material selected from thegroup consisting of cermet materials, polycrystalline diamond,polycrystalline cubic boron nitride, and mixtures thereof. The secondmaterial phase comprises a material that is relatively softer, e.g.,more ductile, than the first material phase. In an example embodiment,the first material phase is formed from polycrystalline diamond and thesecond material phase is formed from cemented tungsten carbide.

The ordered structure of the granules are formed while the granules arein a green state, and the granules can be combined with one another withor without a continuous binder. The combined granules are consolidatedand sintered to provide a final material microstructure comprising arandom arrangement of the granules, on a macro scale, and an orderedarrangement of material phases making up the granules, on a micro scale.The composite material microstructure of a random arrangement of suchgranules operates synergistically to impair crack propagation throughthe composite construction, thereby providing a desired improvement inmaterial toughness.

DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention willbecome appreciated as the same becomes better understood with referenceto the specification, claims and drawings wherein:

FIG. 1 is a schematic photomicrograph of a region of conventionalcemented tungsten carbide;

FIG. 2 is a perspective side view of a first embodiment orderedmulti-material phase component useful for forming randomly-orientedcomposite constructions of this invention;

FIG. 3 is a perspective cross-sectional side view of a second embodimentordered multi-material phase component useful for formingrandomly-oriented composite constructions of this invention;

FIG. 4 is a schematic view of a number of granules formed from the firstembodiment ordered multi-material phase component of FIG. 2;

FIG. 5 is a schematic photomicrograph of a region of a first embodimentrandomly-oriented composite construction of this invention comprising acombined plurality of the granules of FIG. 4;

FIG. 6 is a schematic photomicrograph of a region of a second embodimentrandomly-oriented composite construction of this invention comprising acombined plurality of the granules of FIG. 4 disposed within acontinuous matrix binder material;

FIG. 7 is a perspective side view of an insert for use in a roller coneor a hammer drill bit comprising a randomly-oriented compositeconstruction of this invention;

FIG. 8 is a perspective side view of a roller cone drill bit comprisinga number of the inserts of FIG. 7;

FIG. 9 is a perspective side view of a percussion or hammer bitcomprising a number of inserts of FIG. 7;

FIG. 10 is a schematic perspective side view of a polycrystallinediamond shear cutter comprising a substrate and/or cutting surfaceformed a randomly-oriented composite construction of this invention; and

FIG. 11 is a perspective side view of a drag bit comprising a number ofthe shear cutters of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

Composite constructions of this invention have a specifically engineeredmaterial microstructure comprising a plurality of randomly arrangedparticles or granules that each itself includes an ordered arrangementof two or more continuous material phases. This random arrangement ofsuch granules provides a microstructure having improved properties ofchipping resistance and toughness when compared to conventional singlephase cermet material constructions, and when compared to compositeconstructions having structural units arranged in an ordered or orientedfashion.

Cermet materials are materials that comprise both a ceramic material anda metal material. Examples ceramic materials useful for formingcomposite constructions of this invention generally include carbides,borides, nitrides, diamond, and cubic boron nitride. An example cermetmaterial is cemented tungsten carbide (WC-Co) that is made from tungstencarbide (WC) grains and cobalt (Co). Another class of cermet materialsis polycrystalline diamond (PCD) and polycrystalline cubic boron nitride(PCBN) that are synthesized by high temperature/high pressure processes.

FIG. 1 illustrates a material microstructure for conventionalsingle-phase cemented tungsten carbide 10. Such conventional materialmicrostructure comprises tungsten carbide grains 12 that are bonded toone another by a cobalt phase 14. As illustrated, the tungsten carbidegrains can be bonded to other grains of tungsten carbide, thereby havinga tungsten carbide/tungsten carbide interface, and/or can be bonded tothe cobalt phase, thereby having a tungsten carbide/cobalt interface.The unique properties of cemented tungsten carbide result from thiscombination of a rigid carbide network with a tougher metalsubstructure. The generic microstructure of cemented tungsten carbide, aheterogeneous composite of a ceramic phase in combination with a metalphase, is similar in all cermets.

The relatively low fracture toughness of cemented tungsten carbide hasproved to be a limiting factor in more demanding applications, such asinserts in roller cone rock bits, hammer bits and drag bits used forsubterranean drilling and the like. It is possible to increase thetoughness of the cemented tungsten carbide by increasing the amount ofcobalt present in the composite. The toughness of the composite mainlycomes from plastic deformation of the cobalt phase during the fractureprocess. Yet, the resulting hardness of the composite decreases as theamount of ductile cobalt increases. In most commonly used cementedtungsten carbide grades, cobalt is no more than about 20 percent byweight of the total composite.

As evident from FIG. 1, the cobalt phase is not continuous in theconventional cemented tungsten carbide microstructure, particularly incompositions having a low cobalt concentration. The conventionalcemented tungsten carbide microstructure has a relatively uniformdistribution of tungsten carbide grains in a cobalt matrix. Thus, acrack propagating within the composite will often travel through theless ductile tungsten carbide grains, either transgranularly throughtungsten carbide/cobalt interfaces or intergranularly through tungstencarbide/tungsten carbide interfaces. As a result, cemented tungstencarbide often exhibits gross brittle fracture during more demandingapplications, which may lead to catastrophic failure.

Composite constructions of this invention are formed from a plurality ofparticles, e.g., granules, that are each specifically formed having anordered arrangement of two or more material phases, e.g., a hard phasematerial and a relatively softer or binder phase material. The particlematerial phases can be formed from different materials or can be formedfrom the same general type of material present in a different materialproportion and/or having a different grain size to render a desiredrelative difference in hardness and or ductility.

As used herein, the term “ordered” is understood to refer to the factthat the material phases of the particle are not combined with oneanother in a random manner. Rather, the material phases areintentionally arranged in a predetermined manner to form differentrespective portions or distinct regions of the particle. In each case,the material phases are ordered in the sense that they each occupy thesame distinct portion or region of each particle, thus are arranged orcombined together in a predetermined, rather than a random, fashion. Insome cases, the ordered arrangement of the particle material phases canbe oriented relative to say an axis or other common reference point ofthe particle.

The particle or granule hard material phase can be formed from the groupof materials including cermet materials, PCD, PCBN and the like, and thegranule relatively softer material phase can be formed from differentmaterials such as metals and metal alloys. Alternatively, the hard andsoft material phases can be formed from the same general type ofmaterials, having different material proportions and/or grain sizes asneeded to make one material phase relatively softer and/or more ductilethan the other. For example, the relatively softer granule materialphase can be formed from the same type of material used to form theharder granule material phase, only having a larger proportion of ametal or metal alloy constituent.

Depending on the particular invention application, the material phasesused to form the particles or granules can take on different geometricforms. In one example embodiment, the hard material phase can beprovided in the form of a centrally-located core, and the relativelysofter material phase can be provided in the form of a shell that atleast partially surrounds the core, or visa versa. Alternatively, thehard and soft material phases can each be provided in the form ofdifferent sheets that are each formed from a respective hard and softmaterial. It is to be understood that the specific shape and/or mannerin which the particle material phases are arranged can and will varydepending on the particular composite construction application.

As mentioned above, the fracture toughness of conventional cementedtungsten carbide or other cermets is generally controlled by the ductilemetal binder (e.g., cobalt) component of the material. Plasticdeformation of the binder phase during the crack propagation processaccounts for more than 90 percent of the fracture energy. A problem knowto occur during the manufacture of certain conventional cermetconstructions is the depletion of the binder material. Such depletion isgenerally undesired as it operates to reduce the extent to which theductile binder component can participate in mitigating crackpropagation.

Composite constructions of this invention are specifically designed tohave a material microstructure comprising a three-dimensional networkmade up of a randomly oriented arrangement of the particles. Asmentioned above, each of the particles comprise an ordered arrangementof two or more materials phases. This intentionally configured materialmicrostructure operates to provide an improved degree of chippingresistance, i.e., resistance to crack propagation. The improvement inchipping resistance is due to the increased amount of energy that isrequired to propagate a crack through the microstructure as a result ofthe ordered arrangement of material phases. Composite constructions ofthis invention benefit from the short range ordering of the particlesthat operate to reduce local chipping and minimize crackingperpendicular to the working surface due to the random distribution ofordered segments disposed along the working surface.

For example, a roller cone rock bit insert comprising compositeconstructions of this invention, i.e., having the composite constructiondisposed along an insert working surface, are known to display improvedproperties of chipping resistance and increased fracture toughness whencompared to conventional cemented tungsten carbide compositions, therebyresulting in extended service life.

As discussed briefly above, the ordered arrangement of material phasesforming particles or granules useful for forming composite constructionsof this invention may be derived from differently configuredmulti-material phase components. U.S. Pat. No. 4,772,524 discloses atleast two such components found to be particularly useful in formingcomposite constructions of this invention, which patent is herebyincorporated by reference.

FIG. 2 illustrates a first embodiment ordered multi-material phasecomponent 16 useful for forming composite constructions of thisinvention. The component 16 is provided in the form of a cased or coatedfiber 18. Each fiber 18 comprises a core 20 formed from the one of thematerial phases, that is surrounded by a shell or casing 22 formed fromthe other of the material phases. The core can be formed from the hardor soft material phase, depending on the specific application. In anexample embodiment, the core is formed from the hard material phase andthe shell is formed from the relatively softer material phase. The shellor casing can be applied to each respective core by the method describedin U.S. Pat. No. 4,772,524, or by other well known spray or coatingprocesses. Additionally, “Flaw Tolerant, Fracture Resistant, Non-BrittleMaterials Produced Via Conventional Powder Processing,” (MaterialsTechnology, Volume 10 1995, pp. 131-149), which is also incorporatedherein by reference, describes an extrusion method for producing suchcoated fibers 18.

In an example embodiment, the multi-material phase component 16comprises a core 20 of tungsten carbide and cobalt powder surrounded bya shell 22 of cobalt metal. A green-state component 16 having theordered shell and core arrangement is produced in the following manner.The fibers are fabricated from a mixture of powdered WC-Co, powdered Co,and thermoplastic binder such as wax by the extrusion process identifiedabove. In an example embodiment, the fibers 18 have a WC-Co core 20thickness in the range of from about 30 to 300 micrometers, surroundedby a shell 22 of cobalt having a thickness in the range of from about 3to 30 micrometers. The binder may be as much as 50 percent by volume ofthe total mixture. Tungsten carbide powder and cobalt powder areavailable in micron or submicron sizes, although it is desired that thetungsten carbide powder have a particle size of less than about 20micrometers.

As will be better described below, the extruded green-state component isthen chopped up to form granules having a desired granule length in therange of from about 50 to 1,000 micrometers, and more preferably in therange of from about 70 to 200 micrometers. While the green-statecomponent used to form the granules has been disclosed and illustratedas being generally cylindrical in configuration, it is to be understoodthat such components can be configured having othergeometrically-configured shapes such as hexagonal, square, triangularand the like, as defined by the particular composite constructionapplication.

Each so-formed granule has an ordered arrangement of a core formed froma first material phase, and a shell surrounding the core formed from asecond material phase. The granules are then combined together in randomfashion while in the green state to provide a green-state compositeconstruction. The green-state product is then dewaxed by heating in avacuum or protective atmosphere to remove the thermoplastic binder. Thedewaxed green-state product, having retained its randomly-orientedmicrostructure, is further heated to an elevated temperature near themelting point of cobalt, to form a solid, essentially void-free integralcomposite construction having the desired randomly-oriented materialmicrostructure.

Although use of a cemented tungsten carbide material and cobalt havebeen described above as example respective component hard phase andbinder phase materials, it is to be understood that such componentsuseful for forming composite constructions of this invention may beformed from many other different materials that are discussed in detailbelow. For example, such components can comprise a hard phase formedfrom PCD or PCBN, and a relatively softer phase formed from the samegeneral material or from a different material such as cemented tungstencarbide or cobalt metal. In such example, the core 20 can be formed froma PCD or PCBN composition according to the process described in U.S.Pat. Nos. 4,604,106; 4,694,918; 5,441,817; and 5,271,749 that are eachincorporated herein by reference, starting with diamond or cBN powderand wax. Each PCD core 20 is surrounded by a cemented tungsten carbideor cobalt metal shell 22 to form the fiber 18. In an example embodiment,the fibers have a PCD core thickness in the range of from about 30 to300 micrometers, and the shell has a thickness in the range of fromabout 3 to 30 micrometers.

FIG. 3 illustrates a second embodiment ordered multi-material phasecomponent 24 useful for forming composite constructions of thisinvention. The component 24 comprises a repeating ordered arrangement ofmonolithic sheets of a hard material phase 26, and sheets of arelatively softer material phase 28 that can be stacked one on top ofanother, or that can be arranged to produce a swirled or coiledcomposite construction. In an example embodiment, the green-statecomponent 24 comprises sheets 26 that are formed from a powdered cermetmaterial, and sheets 28 that are formed from a powdered metal. Athermoplastic binder is added to both powder sheets 26 and 28 forcohesion and to improve the adhesion between the adjacent sheets. Thesheets 26 of the hard material phase and the sheets 28 of the bindermaterial phase are alternately stacked on top of one another and coiledinto a rod 30 having a spiral cross section. Additionally, depending onthe desired composite construction properties for a particularapplication, the sheets 26 and 28 may be formed from more than one typeof hard material and/or more than one type of binder material phase, andcan be stacked in random fashion, to form the second embodimentcomponent 24.

In an example embodiment, the sheets 26 are formed from powdered WC-Co,and the sheets 28 arc formed from powdered cobalt. Alternatively, thesheets 26 can be formed from PCD or PCBN, and the sheets 28 can beformed from a relatively more ductile binder material such as metals,metal alloys, cermets and the like. The WC-Co sheets 26 are formedhaving a thickness in the range of from about 50 to 300 micrometers, andthe cobalt sheets 28 are formed having a thickness in the range of fromabout 5 to 10 micrometers after consolidation.

As will be better described below, the coiled green-state component isthen chopped up to form granules having the desired granule length notedabove. Each so-formed granule has an ordered arrangement of sheets 26and 28 coiled around one another. The granules are then combinedtogether in random fashion while in the green state to provide agreen-state composite construction. The green-state product is thendewaxed by heating in a vacuum or protective atmosphere to remove thethermoplastic binder. The dewaxed green-state product, having retainedits randomly-oriented microstructure, is further heated to an elevatedtemperature near the melting point of cobalt, to form a solid,essentially void-free integral composite construction having the desiredrandomly-oriented material microstructure.

FIG. 4 illustrates a number of granules 30 that are formed from thefirst embodiment ordered multi-material phase component discussed aboveand illustrated in FIG. 2. The granules 30 are formed while thecomponent is in the green state, and the specific granule size isunderstood to vary depending on the particular composite constructionapplication. Each granule 30 comprises an ordered arrangement of firstand second material phases. Specifically, the granule core 32 is formedfrom the first material phase, and the granule shell 34 surrounding thecore is formed from the second material phase.

FIG. 5 illustrates a region of a first embodiment randomly-orientedcomposite construction 36 of this invention comprising athree-dimensional arrangement of granules 38 that have been combinedwith one another in a random fashion. As illustrated, this composite ischaracterized by bonding that takes place between the adjacent surfacesof the granules themselves, e.g., between adjacent granule core portions40, between adjacent granule shell portions 42, and between adjacentgranule core 40 and shell 42 portions, depending on the particularorientation of the granules relative to one another.

It is theorized that this random arrangement of differently bondedtogether granules, each comprising an ordered arrangement of materialphases, operates to provide a tortuous and/or discontinuous path withinthe material microstructure to help deflect, absorb, and blunt cracksthat may travel therethrough, thereby operating to control crackpropagation and provide a composite construction having properties ofimproved fracture toughness and resistance to chipping reduce crackpropagation when compared to conventional cermet constructions.

Randomly-oriented composite constructions of this invention have crackinhibiting structures both on the micro and macro scale. On the microscale, the ordered microstructure of the particles operate to inhibitcracks on the surface. In an example embodiment, where the orderedmicrostructure is provided in the form core and shell configuration,this ordered material microstructure presents a first layer of crackpropagation resistance due to the changing material properties (e.g.,stiffness and toughness) that is developed locally. This type of orderedmaterial structure is known to display improved diamond retention due tothe minimization of cracking, and hence minimization of spalling.Composite constructions of this invention take advantage of suchimproved properties associated with the ordered microstructure and thenimprove on them. Specifically, by taking the core and shell orderedstructure, chopping the structure into granules, and then combining thegranules together in a random fashion. On a macro scale, this randomcombination of ordered granules operates to further interrupt andinhibit crack propagation between the granules (through core-to-core,core-shell, or shell-shell interaction) and, thus through the structure.

FIG. 6 illustrates a region of a second embodiment randomly-orientedcomposite construction 44 of this invention comprising athree-dimensional arrangement of granules 46 that have been combinedwith one another in a random fashion. Unlike the first embodimentcomposite construction described above and illustrated in FIG. 5, thissecond embodiment composite construction 44 comprises the plurality ofrandomly-oriented granules 46 disposed within a continuous matrix binderphase 48. The binder phase 48 can be formed from the same types ofmaterials useful for forming the granule first or second materialphases; and is used to provide an insulating phase between the granules,bonding the granules to one another.

As illustrated in FIG. 6, this second embodiment composite constructionis characterized by bonding that takes place between the insulatingbinder phase 48 and the plurality of granules 46. Accordingly, ratherthan the granule core and shell portions being bonded to core and/orshell portions of adjacent respective granules, the granule and coreportions are ideally bonded only to the binder phase material. It is tobe understood, however, the there may be some locations in the materialmicrostructure where granule-to-granule bonding does occur.

In this particular embodiment, it is theorized that random arrangementof granules, each comprising an ordered arrangement of material phases,in combination with the insulating continuous binder phase operates toprovide an enhanced crack propagation path within the composite, therebyproviding a composite construction having properties of improvedfracture toughness and resistance to chipping to control and reducecrack propagation when compared to conventional cermet constructions. Inthis particular embodiment, the ordered material phase of the granulesoperates as described above to inhibit crack propagation. Additionally,the insulating binder operates to still further inhibit crackpropagation by physically separating the randomly arrange of granulesfrom one another.

Composite constructions of this invention are unique in that theycomprise a randomly-oriented microstructure made from components thatthemselves have an ordered arrangement of multiple material phases. Thecombined random arrangement of granules, on a relatively macro scale,that each have an ordered material phase on a relatively micro scale,produces a synergistic effect that operates to provide improvedperformance properties of wear resistance, resistance to chipping andfracture toughness that exceeds those of either exclusivelyrandomly-oriented or exclusively ordered composite compositions.

In order to ensure the production of a final composite compositionhaving these improved properties, it is essential that the desiredcombination of a randomly-oriented arrangement of granules themselveshaving an ordered arrangement of material phase be retained during theprocess of making the composite construction. Thus, compositeconstructions of this invention are made by first constructinggreen-state components, e.g., granules, having the desired orderedarrangement of two or more material phases, combining the granules in arandomly-oriented manner, and then consolidating and sintering thecombined green-state granules. To ensure the desired microstructure ofthe finished composite construction, it is important that each of theabove-noted steps be carried out so that the random and ordered featuresof the construction be maintained, i.e., in a manner that does notpermit appreciable migration between the material phases.

As noted above, a processing agent or binder material can be used to aidin the process of forming the green state components. Such processingagent can be used to help form one or both granule material phasesand/or to help form the composite construction itself. Suitableprocessing agents include thermoplastic materials, thermoset materials,aqueous and gelation polymers, as well as inorganic binders. Suitablethermoplastic polymers include polyolefins such as polyethylene,polyethylene-butyl acetate (PEBA), ethylene vinyl acetate (EVA),ethylene ethyl acetate (EEA), polyethylene glycol (PEG),polysaccharides, polypropylene (PP), poly vinyl alcohol (PVA),polystyrene (PS), polymethyl methacrylate, poly ethylene carbonate(PEC), polyalkylene carbonate (PAC), polycarbonate, poly propylenecarbonate (PPC), nylons, polyvinyl chlorides, polybutenes, polyesters,waxes, fatty acids (stearic acid), natural and synthetic oils (heavymineral oil), and mixtures thereof.

Suitable thermoset plastics include polystyrenes, nylons, phenolics,polyolefins, polyesters, polyurethanes. Suitable aqueous and gelationsystems include those formed from cellulose, alginates, polyvinylalcohol, polyethylene glycol, polysaccharides, water, and mixturesthereof. Silicone is an example inorganic polymer binder. An exemplarypolymer binder for forming the green-state fiber component is ethylenevinyl acetate and heavy mineral oil, which is preferred because of itsability to be extruded and pultruded in fine fibers. In addition, thebackbone (EVA) is insoluble in heptane and alcohol.

Consolidation techniques useful for forming composite constructions ofthis invention include solid-state consolidation methods such as hotpressing, hot isostatic pressing (HIPing) as described in U.S. Pat. No.5,290,507 that is incorporated herein by reference, and rapidomnidirectional compaction (ROC) as described in U.S. Pat. Nos.4,945,073; 4,744,943; 4,656,002; 4,428,906; 4,341,577 and 4,124,888which are each incorporated herein by reference.

Broadly speaking, the ROC process can be used to form compositeconstructions of this invention and involves pressing the green-stateproduct, i.e., the randomly-oriented arrangement of granules in a closeddie to a desired shape, such as a rock bit insert or a cap that forms aworking surface of a rock bit insert. The resulting “green” insert isthen vacuum dewaxed and presintered at a relatively low temperature toachieve a density appreciably below full theoretical density. Thepresintering is only sufficient to permit handling of the insert forsubsequent processing. The green insert is wrapped in a first containerand is then placed in second container made of a high temperature highpressure self-sealing ceramic material. The second container is filledwith a special glass powder and the green part disposed within the firstcontainer is embedded in the glass powder. The glass powder has a lowermelting point than that of the green part, or of the ceramic die.

The second container is placed in a furnace to raise it to the desiredconsolidation temperature, that is also above the melting point of theglass. For example, for a green state composite construction comprisinga random arrangement of granules made up of a WC-Co hard phase andcobalt ductile metal phase system, the consolidation temperature is inthe range of from 1,000° C. to 1,280° C. The heated second containerwith the molten glass and green part immersed inside is placed in ahydraulic press having a closed cylindrical die and a ram that pressesinto the die. Molten glass and the green part are subjected to highpressure in the sealed ceramic container. The part is isostaticallypressed by the liquid glass to pressure as high as 120 ksi. Thetemperature capability of the entire process can be as high as 1,800° C.The high pressure is applied for a short period of time, e.g., less thanabout five minutes and preferably one to two minutes, and isostaticallycompacts the green part to essentially 100 percent density.

Conventional liquid phase consolidation techniques are generally notthought to be useful for forming composite constructions of thisinvention because of the tendency for the binder material within thegranules to migrate, thereby causing the granule ordered material phasesto become distorted or unoriented. However, liquid phase consolidationtechniques may be used that operate under conditions of reducedtemperature. For example, reactive liquid phase sintering relates to aprocess whereby one or more of the constituent elements is capable ofreleasing energy upon formation (i.e., enthalpy formation is high). Thisenergy is released as heat which can (if conditions are proper) producea self-propagating reaction that will consolidate the component at arelatively low temperature (that being the temperature needed toinitiate the reaction). Thus, randomly-oriented composite constructionsof this invention can be formed using such technique if one of thegranule material phases contains an element that, upon reaching anignition temperature, will operate to densify the entire component. Thistechnique is nonreversible, meaning that the reaction product will notgo to liquid due to an increased melting point of the compound incomparison to its constituent elements.

Supersolidus liquid phase sintering is another technique that can beused to consolidate composite constructions of this invention, whereby acomposition will yield upon heating a mixture of liquid and solidphases. This technique has the advantage over conventional liquid phasesintering of allowing for densification at lower temperatures andprovides for improved control over distortion since the operatingtemperature dictates the yield of the liquid. Hence a composition can becontrived where one phase develops supersolidus liquid phase sinteringconditions and infiltrates another phase, thereby causing the entirestructure to densify. Alternatively, each of the granule material phasesforming the composite construction can have materials capable ofsupersolidus liquid phase sintering.

Other solid-state consolidation techniques useful for making compositeconstructions of this invention include those incorporating a rapidheating step such as microwave sintering, plasma-activated sintering,and other types of field-assisted sintering. Each of these techniquesare effective at producing a final composite construction having theretained randomly-oriented granule microstructure.

Examples of consolidation techniques using rapid heating methods includefield-assisted sintering and laser heating. Field-assisted sinteringuses an electromagnetic field to generate rapid heating and improvedsurface transport. Often time, energy that is provided from theelectromagnetic field is concentrated on surface asperities. Severalheating techniques for conducting field-assisted sintering exist,including but not limited to induction heating, microwave, plasma andelectric discharge. Induction sintering uses alternating current tocreate a magnetic field within the material to induce eddy currents.These eddy currents serve to rapidly heat a component.

Similarly, microwave sintering allows for rapid heating of a componentbased on its (or susceptor) material properties. A susceptor is amaterial that will do the heating by either induction or microwaveprocess when the compact is either nonconductive or transparent tomicrowave. Besides rapid heating, microwave sintering is believed toprovide lower activation energies for diffusion and promote steepconcentration gradients (operating to further increase diffusivity).Microwave sintering or microwave-assisted sintering are consolidationtechniques, typically carried out at ambient pressure conditions, whichenhances densification because of rapid heating and homogenization ofthe part's internal temperature and creation of plasma at all powderasperities to create an enhanced surface.

Laser heating is another approach that can be used to primarily sinter athin section of powder (wherein the depth of penetration is verylimited) and, hence, is often used for rapid prototyping machines thatbuild layer by layer.

Electrical discharge heating is used to heat a component via electricalresistance. Typically, a hot press is employed since constant contact(pressure) is needed and graphite promotes electrical conduction/heatingof a component. When the electric filed is pulsed, plasma is generatedtherefrom at the asperities. Likewise, plasma sintering is similar inthat an electromagnetic field is generated resulting in an enhanceddiffusion. A secondary type of plasma sintering is to induce an externalplasma using RF heating of gaseous species to promote localized heatingand concentration gradients. However, this system is not as advantageousas the system described below due to the lack of applied pressure.

Plasma-assisted sintering is a technique whereby plasma is generatedwithin the powder compact. This plasma enhances surface activateddiffusion, which promotes densification at lower sintering temperaturesand/or promotes shorter sintering times. The instantaneous electricpulses using high currents generate the plasma. Often theplasma-assisted sintering is operated effectively applied to hotpressing, where the electric field pulses are delivered to the compactaxially through the use of graphite compaction rods. This technique isalso referred to as field-assisted sintering. Field strengths vary fordifferent materials, but generally range in from 18 to 50 V/cm.

Composite constructions having a material microstructure consisting ofrandomly-oriented granules, prepared according to principles of thisinvention, exhibit an improved degree of fracture toughness and chippingresistance when compared to conventional cermet materials such ascemented tungsten carbide, due to the synergistic effect of theplurality of randomly-arranged granules (on the relatively macro scale),and ordered material phases of the granules (on the relatively microscale).

Materials useful for forming the granule hard material phase can beselected from the group of cermet materials including, but not limitedto, carbides, borides and nitrides of the group IVB, VB, VIB, VIIB, andVIII metals and metal alloys of the periodic table (CAS version).Example cermet materials include: WC-M, TiC-M, TaC-M, VC-M, and Cr₃C₂-M,where M is a metal such as Co, Ni, Fe, or alloys thereof as describedabove. A preferred cermet material is WC-Co. The granule hard materialphase can also be formed from PCD, HBN, CBN, PCBN, and mixtures of thesematerials with carbides, borides and nitrides of the group IVB, VB, VIB,VIIB, and VIII metals and metal alloys of the periodic table CASversion). Composite constructions of this invention comprising granuleshaving PCD as the hard material phase are highly desirable in aggressivedrilling applications that call for extreme wear resistance.

In addition to the materials noted above, the granule hard phasematerials can also be formed from a composite construction, i.e., amaterial comprising an ordered or random arrangement of two or moredistinct material phases. Composite constructions useful in this regardinclude those having a double cemented material microstructure. The term“double cemented” as used here refers to the fact that the materialmicrostructure for such construction comprises a plurality of firstphases made up of a cemented material, i.e., a number of hard phaseparticles bonded to one another via a binder phase, and these firstphases are distributed within a substantially continuous second orbinder phase. In an example embodiment, the plurality of first phasesare formed from WC-Co, and the second or binder phase is cobalt.

Because each first phase comprises hard grains bonded together orcemented by a metallic cementing agent, and the first phases arethemselves disposed within a second metallic cementing agent, theoverall material microstructure is referred to as being double cemented.Example double cemented cermet constructions useful for forming thegranule hard material phase include those disclosed in U.S. Pat. No.5,880,382, which is incorporated herein by reference, and which have amaterial microstructure comprising a plurality of first phases (eachformed from the same types of cermet materials discussed above) that aredistributed within a substantially continuous matrix second phase thatis formed from a relatively more ductile material (such as thosematerial discussed above useful for forming the cermet metalliccementing agent).

Double cemented composite constructions useful for forming the granulehard phase can also include PCD, HBN, CBN and PCBN. An example of suchconstruction is one comprising a plurality of first phases in the formof granules comprising PCD, HBN, CBN, of PCBN, wherein the granules areformed by combining a requisite hard grain with a binder material, andwherein the granules are distributed within a substantially continuousmatrix binder phase. In an example embodiment, the double cementedcomposite construction comprises a plurality of granule phases formedfrom PCD, and the continuous matrix binder phase is WC-Co, as disclosedand prepared according to U.S. Pat. No. 6,454,027, which is incorporatedherein by reference.

Materials useful for forming the granule relatively softer or bindermaterial include those materials disclosed above for forming the hardmaterial phase, or different materials. In the event that the selectedgranule relatively softer or binder material phase is the same as thatused to form the granule hard material phase, it is desired that theproportion and/or the grain size of the selected binder material beadjusted so that it be relatively softer or more ductile than the hardmaterial phase. For example, when both the granule hard and softmaterial phases are selected to be WC-Co, the soft material phase WC-Cocan have a higher proportion of cobalt than the hard material phaseWC-Co, and/or the soft material phase WC-Co can have a WC grain sizethat is smaller than that of the hard material phase WC-Co to provide amaterial phase that is relatively softer or more ductile than the hardphase material. Accordingly, it is to be understood that compositeconstructions of this invention can be configured having microstructureof randomly-oriented granules comprising two or more material phasesformed from the same general type of material.

The granule relatively softer material phase can also be formed from amaterial that is different than that used to form the hard phasematerial. Accordingly, materials useful for forming the granulerelatively softer phase include those selected from the group IIIA, IVB,VB, VIB, VIIB, and VIII metals and metal alloys of the periodic table(CAS version), such as Fe, Ni, Co, Cu, Ti, Al, Ta, Mo, Nb, W, and theiralloys. Additionally, the binder phase can be formed from the groupincluding carbides, borides and nitrides of the group IVB, VB, VIB,VIIB, and VIII metals and metal alloys of the periodic table (CASversion), when the granule hard phase material (e.g., the fiber core) isPCD or PCBN because of their properties of good thermal expansioncompatibility and good toughness. For example, the granule binder phasecan be WC-Co when the granule hard phase material is PCD or PCBN. In anexample embodiment, a desired binder phase is cobalt when the hard phasematerial is WC-Co. The above provided materials useful for forming thegranule binder phase material can also be used to form the continuousmatrix binder phase between the granules in the second embodimentrandomly-oriented composite constructions of this invention asillustrated in FIG. 6.

The volume fraction of the continuous binder phase in the secondembodiment composite construction will influence the properties of theoverall composite construction, including wear resistance, fracturetoughness and chipping resistance. The volume fraction of the continuousbinder phase may be in the range of from about 15 to 50 percent byvolume, based on the total volume of the composite construction.Preferably, for composite constructions designed for use in moredemanding applications, the binder phase can be in the range of fromabout 15 to 30 percent by volume of the total volume of the composite.

Composite constructions having a material microstructure ofrandomly-oriented granules, prepared according to principles of thisinvention, will be better understood and appreciated with reference tothe following example:

EXAMPLE Randomly-Oriented PCD Composite Construction

A green-state fiber component was constructed by extrusion processcomprising a core formed from diamond grains having a desired content ofbinder metal, e.g., cobalt, and having a grain size of from about 1 to50 mm. The fiber also had a shell surrounding the core that was formedfrom tungsten carbide-cobalt or diamond grains having materialproperties different from that of the diamond core. The fiber had apre-consolidation outside diameter of approximately 1 mm, a corediameter of approximately 80 μm, and a shell thickness of approximately16 μm. The fiber was chopped into granules having an average axiallength of approximately 500 to 1000 μm. The granules were loaded into arod mold and consolidated at a temperature of approximately 180° C. anda pressure of approximately 42 MPa. The consolidated green-state productwas then sintered by high-temperature, high-pressure process atapproximately 1,400° C., and approximately 5,500 MPa for approximately120 seconds.

The so-formed randomly-oriented composite construction displayed ahardness in the range of between 3,000 and 3,600 HV (n=16; wherein HV isthe hardness units for Vikers hardness), and a granite log wearresistance in the range of between 0.25 and 0.65×10⁶ (n=4; wherein theunit of measurement of wear resistance is volume of granite removeddivided by volume of working surface removed), where higher is more wearresistance.

Composite constructions of this invention are well suited to serve inapplications calling for combined properties of both improved wearresistance and improved fracture toughness, such as tools for mining,machining and construction applications, where the combined mechanicalproperties of high fracture toughness, wear resistance, and hardness arehighly desired. Composite constructions of this invention can be used toform working, wear and/or cutting components in machine tools and drilland mining bits such as roller cone rock bits, percussion or hammerbits, diamond bits, and substrates for shear cutters.

For example, FIG. 7 illustrates an insert 50 for use in a wear orcutting application in a subterranean drilling bit, such as a rollercone drill bit, percussion or hammer drill bit. The insert 50 itself ora portion of its surface may be formed from the composite constructionsof this invention. For example, such inserts can be formed from blanksthat are made from composite constructions of this invention, and thatare pressed or machined to the desired shape of a roller cone rock bitinsert. The shaped inserts are then heated to about 200 to 400° C. invacuum or flowing inert gas to debind the composite, and the inserts arethen sintered at an elevated temperature below the melting point of thebinder phase material, in this case below the melting temperature ofcobalt.

For example, referring to FIG. 8, wear or cutting inserts 50 (shown inFIG. 7) formed from composite constructions of this invention can beused with a roller cone rock bit 51 comprising a body 52 having threelegs 54, and a roller cutter cone 56 mounted on a lower end of each leg.The inserts 50 can be fabricated according to one of the methodsdescribed above. The inserts 50 are provided in the surfaces of thecutter cone 56 for bearing on a rock formation being drilled.

Referring to FIG. 9, inserts 50 formed from composite constructions ofthis invention can also be used with a percussion or hammer bit 58,comprising a hollow steel body 60 having a threaded pin 62 on an end ofthe body for assembling the bit onto a drill string (not shown) fordrilling oil wells and the like. A plurality of the inserts 48 areprovided in the surface of a head 64 of the body 60 for bearing on thesubterranean formation being drilled.

Referring to FIG. 10, composite constructions of this invention can alsobe used to form PCD shear cutters 66 that are used, for example, with adrag bit for drilling subterranean formations. More specifically,composite constructions of this invention can be used to form a shearcutter substrate 68 that is used to carry a layer of PCD 70 that issintered thereto or, alternatively, the entire substrate and cuttingsurface can be made from the composite construction.

Referring to FIG. 11, a drag bit 72 comprises a plurality of such PCDshear cutters 66 that are each attached to blades 74 that extend from ahead 76 of the drag bit for cutting against the subterranean formationbeing drilled.

Although, limited embodiments of composite constructions having amaterial microstructure of randomly-arranged granules, each having anordered arrangement of two or more material phases, methods of makingthe same, and applications for the same, have been described andillustrated herein, many modifications and variations will be apparentto those skilled in the art. For example, although compositeconstructions have been described and illustrated for use with rockbits, hammer bits and drag bits, it is to be understood that compositesconstructions of this invention are intended to be used with other typesof mining and construction tools comprising wear or cutting surfaces.Accordingly, it is to be understood that within the scope of theappended claims, composite constructions according to principles of thisinvention may be embodied other than as specifically described herein.

1. A bit for drilling subterranean formations comprising a body and anumber of cutting elements connected to the body, wherein one or more ofthe cuffing elements comprises a composite construction comprising aplurality of first regions and a second region that surrounds at least aportion of the first regions, wherein composite construction is formedby the process of: combining a plurality of randomly arranged granuleseach comprising a first material phase and a second material phase,wherein the first and second material phases are in contact with oneanother and are oriented relative to one another the same within eachgranule, wherein the granule first and second material phases are formedfrom materials selected from the group consisting of polycrystallinediamond, polycrystalline cubic boron nitride, precursors of thesematerials, and mixtures thereof, and wherein the granule second materialphase is relatively more ductile than the granule first material phasein sintered form; and subjecting the combined randomly arranged granulesto elevated pressure and temperature conditions to form the compositeconstruction.
 2. The bit as recited in claim 1 wherein the plurality offirst phases comprises diamond crystals.
 3. The bit as recited in claim2 wherein the second phase comprises diamond crystals.
 4. The bit asrecited in claim 2 wherein the volume content of diamond crystals in thefirst phase is different from that in the second phase.
 5. The bit asrecited in claim 2 wherein the diamond grains used to form the granulefirst material phase have an average size that is different from thediamond grains used to form the granule second material phase.
 6. Thebit as recited in claim 1 wherein the granule first material phase is acore and the granule second material phase is a shell that surrounds atleast a portion of the core.
 7. The bit as recited in claim 1 whereinafter the step of combining the granules, at least a portion of thefirst or second material phase of one or more granules is in contactwith a portion of a same material phase of an adjacent granule.
 8. Thebit as recited in claim 1 wherein the composite construction furthercomprises a third region that is substantially continuous, and whereinthe plurality of first regions and the second region surrounding theplurality of second regions are disposed within the third region.
 9. Thebit as recited in claim 8 wherein the third region is formed from cermetmaterials, polycrystalline diamond, polycrystalline cubic boron nitride,precursors of these materials, and mixtures thereof.
 10. The bit asrecited in claim 1 further comprising a number of blades extendingoutwardly from the body, and wherein the number of cutting elements areattached to one or more of the blades.
 11. The bit as recited in claim 1wherein the body includes: at least one journal pin extending from a legof the body; and a cutter cone rotatably mounted on the pin; wherein thecutting elements are attached to the cone.
 12. A composite constructioncomprising a sintered plurality of randomly oriented granules forming amaterial microstructure comprising a plurality of first regions disposedwithin a substantially continuous second region, wherein the firstregions are formed from granule cores selected from the group ofmaterials consisting of [cermet materials,] polycrystalline diamond,polycrystalline cubic boron nitride, precursors of these materials, andmixtures thereof, and the second region is formed from granule shellsdisposed around at least a portion of a respective granule cores, thegranule shells being selected from the group of materials consisting of[cermet materials,] polycrystalline diamond, polycrystalline cubic boronnitride, precursors of these materials, and mixtures thereof, andwherein at least a portion of the core or shell of one or more, granulesis in contact with a portion of the core or shell of an adjacentgranule.
 13. The composite construction as recited in claim 12 whereinthe composite construction comprises a cellular construction wherein theplurality of first regions are substantially surrounded by the secondregion.
 14. The composite construction as recited in claim 12 whereinthe first and second regions each comprise diamond crystals.
 15. Thecomposite construction as recited in claim 14 wherein the diamond volumecontent in the first region is different than the diamond volume contentin the second region.
 16. The composite construction as recited in claim14 wherein the average diamond crystal size in the first region isdifferent than the average diamond crystal size in the second region.17. A method for making a composite construction comprising a cellularmaterial microstructure including a plurality of first regions disposedwithin a second region comprising the steps of: combining a plurality ofrandomly arranged granules each comprising a core phase and a shellphase that is in contact with and at least partially surrounds the corephase, wherein the core and shell phases of each granule are positionedthe same relative to one another for each granule, wherein the granulesare combined so that a core or shell phase of one or more granules is incontact with the core or shell phase of one or more adjacent granules,wherein the core and shell phases are formed from materials selectedfrom the group consisting of [cermet materials,] polycrystallinediamond, polycrystalline cubic boron nitride, precursors of thesematerials, and mixtures thereof, wherein the core phase is formed from amaterial having a sintered hardness different from that of the shellphase; subjecting the combined plurality of granules to elevatedpressure and temperature conditions to consolidate and sinter thegranules to form the composite construction.
 18. The method as recitedin claim 17 wherein a population of the composite construction pluralityof first regions are completely surrounded by the second region.
 19. Themethod as recited in claim 17 wherein the granule core and shell phaseeach comprise a diamond material.
 20. The method as recited in claim 19wherein the granule core comprises a diamond volume content that isdifferent from that of the granule shell.